Recently, the III-V compounds, such as GaAs, having larger bandgaps than that of Si, are used for fabricating schottky diodes. Such schottky diode structures having larger bandgaps and carrier mobilities are often applied in rectifiers or transistors used in high-speed communication systems.
FIGS. 1(a) and 1(b) illustrate structures of schottky diode structures, each of which includes a substrate 1, an epitaxial layer 2 and a metal layer 3. A schottky barrier is formed at the junction of the metal layer 3 and the epitaxial layer 2. In a schottky diode manufacturing process, the surface state, surface oxidation, concentrations of background impurities and the existence of defects of the epitaxial layer 2 will affect the potential barrier of the schottky barrier greatly. The schottky barrier pinning phenomena caused by the high surface state and concentration of the deep impurities will limit the potential barrier of the schottky barrier under some specified value, about 0.8 eV for GaAs, for example. Furthermore, the reverse breakdown voltage of a schottky is also affected by the background impurity concentration, while the reverse leakage current is determined by the conditions of the factors mentioned above. Accordingly, it is conceivable to lower the surface state density or the impurity concentration of the epitaxial layer for increasing the height of the schottky barrier and the reverse breakdown voltage and lowering the reverse leakage current.